Power train control system

ABSTRACT

A control system is shown for a multispeed forward and reverse track-laying vehicle power train, the control system having a manual forward and reverse control for effecting manual shifts between forward and reverse, a manual drive range control and an automatic drive range control for effecting manual and automatic drive range shifting operation and a steering control for effecting s steering operation. The manual forward and reverse control provides selection between forward and reverse drive in the lowest drive range and prevents such shifting by the operator in all of the higher drive ranges. The manual drive range control provides selection between the drive ranges with the selected drive range being established immediately on an upshift and by speed governed automatic shifting operation on a downshift. The automatic drive range control provides automatic shifting using separate speed controlled upshift biases, an engine torque demand controlled upshift inhibiting bias and an engine torque demand controlled downshift bias. Both the manual forward and reverse control and the manual drive range control are electrically activated and in the event there is an interruption in electrical power, the directional drive selected by the manual forward and reverse control is maintained while the range control, if under manual control, is automatically conditioned for automatic control to maintain power train control. A sequence control is effective to disengage the range drive to the load in the lowest drive range during shifting between forward and reverse to provide for engagement of the directional drive under no-load conditions. The steer control operates on a hydrostatic unit to control steering by controlling hydrostatic pump displacement while assuring straight vehicle no-drift motion when there is no steer demand. The controlling force effecting this pump displacement control is varied according to hydrostatic pump output to meet the varying steer load demands in both directions of steer. There is also provided a stroke or pump displacement limiter for limiting pump displacement regardless of the steer demanded by the operator to prevent pump overload. Hydrostatic system pressure is controlled by a pressure relief control in accordance with engine torque demand and vehicle speed to both prevent overloading of the hydrostatic pump and limit the degree of steer bias. The steer control signals the range control to inhibit automatic range shifting during steering operation. The hydrodynamic torque converter in the power train has a lockup drive which is normally disengaged on range shifting and is held engaged during low speed operation in each range to provide for utilization of vehicle momentum to provide power for steering while preventing engine stall.

United States Eatent 91 Schaefer [45] Apr. 10, 1973 POWER TRAIN CONTROL SYSTEM [75] Inventor: Robert H. Schaefer, Westfield, Ind.

[73] Assignee: General Motors Corporation, De-

troit, Mich.

[22] Filed: Aug. 7, 1970 [21] Appl. No.: 61,981

Related US. Application Data [60] Division of Ser. No. 779,502, Nov. 27, 1968,

Pat. NO. 3,640,157.

[52] US. Cl. ..60/488, l80/6.48, 60/459 [51] Int. Cl. ..F16d 31/06, B62d 11/00 [58] Field of Search ..l80/6.48, 6.44, 6.3;

60/19, 52 S, 52 NS, 53 R [56] References Cited UNITED STATES PATENTS 3,383,857 5/1968 Rajchel et al ..60/53 A 3,393,509 7/1968 Kempson ..60/53 R Primary Examiner-Edgar W. Geoghegan Att0meyE. W. Christen et al.

[5 7 ABSTRACT A control system is shown for a multispeed forward and reverse track-laying vehicle power train, the control system having a manual forward-and reverse control for effecting manual shifts between forward and reverse, a manual drive range control and an automatic drive range control for effecting manual and automatic drive range shifting operation and a steering control for effecting s steering operation. The manual forward and reverse control provides selection between forward and reverse drive in the lowest drive range and prevents such shifting by the operator in all of the higher drive ranges. The manual drive range control provides selection between the drive ranges with the selected drive range being established immediately on an upshift and by speed governed automatic shifting operation on a downshift. The automatic drive range control provides automatic shifting using separate speed controlled upshift biases, an engine torque demand controlled upshift inhibiting bias and an engine torque demand controlled downshift bias. Both the manual forward and reverse control and the manual drive range control are electrically activated and in the event there is an interruption in electrical power, the directional drive selected by the manual forward and reverse control is maintained while the range control, if under manual control, is automatically conditioned for automatic control to maintain power train control. A sequence control is effective to disengage the range drive to the load in the lowest drive range during shifting between forward and reverse to provide for engagement of the directional drive under no-load conditions/The steer control operates on a hydrostatic unit to control steering by controlling hydrostatic pump displacement while assuring straight vehicle no-drift motion when there is no steer demand. The controlling force effecting this pump displacement control is varied according to hydrostatic pump output to meet the varying steer load demands in both directions of steer. There is also provided a stroke or pump displacement limiter for limiting pump displacement regardless of the steer demanded by the operator to prevent pump overload.

Hydrostatic system pressure is controlled by a pressure relief control in accordance with engine torque demand and vehicle speed to both prevent overloading of the hydrostatic pump and limit the degree of steer bias. The steer control signals the range control to inhibit automatic range shifting during steering operation. The hydrodynamic torque converter in the power train has a lockup drive which is normally disengaged on range shifting and is held engaged during low speed operation in each range to provide for utilization of vehicle momentum to provide power for steering while preventing engine stall.

2 Claim, 9 Drawing Figures PATENTED 1 @1973 3,726,094

sum 1 OF e PRIME MOVER GOVERNOR 42 &

INVENTUR. BY Ruiz/f H Mae/2r ATTORNEY RTER PRESSURE REGULATOR VALVE PATENTEUAPR 1 01975 3 726,094

SHEET 2 BF 6 MANUAL SIGNAL VALVE G. I. ACCUMULATOR l-Z SHIFT VALVE 3- 4 SHIFT VALVE 1 N VEN TOR.

Y yak/f H Sake/er ATTORNEY PATEHTEUAFMOEH 37261194 SHEET 3 BF 6 AUTOMATIC SHIFT INHIBITOR VALVE TV. VALVE AIR VALVE LOCKUP VALVE AND REVHSE MAIN PRESSURE REGULATOR VALVE MAIN PRESSURE REGULATOR INVENTOR.

AT TORNEY PATENTEUAPR1 01915 3. 726,094

SHEET 4 0F 6 Q HYDROSTATIC MOTOR CENTERING AND STEER SIGNAL Dc'VlCE INVENTOR.

75a g?) Hahn? H. 5c/iaefer ATTORNEY PATENTEB PP 0 Km 3', 726 094 sum 5 or 6 FORWARD AND REVERSE SHIFT VALVE SEQUENCE VALVE FORWARD AND REVERSE SHIFT lNHlBlTOR VALVE IN VEN TOR.

w BY Hahn H. 5c/mefer if; & 6 W 4 XAM ATTORNEY PATENTEUAPR 1 01975 SHEET 8 OF 6 r. e R 0 Mr. V mun f w 0 5 R0 f B 5 W XXXX W m X X X X X X L 8 v m X X X X 3 m X X 0 8 M X X E Z X X 4 N C C m H L I L M A WN 4 J2 mW4 m M m w T w A N U N m A REVERSE RWARD ORNEY POWER TRAIN CONTROL SYSTEM This application is a division of application Ser. No. 779,502, filed Nov. 27, 1968, now US. Pat. No. 3,640,157, granted Feb.8, 1972.

This invention relates to power train or transmission control systems and more particularly to a control system for a track-laying vehicle power train providing manual shift control, automatic shift control and steering control.

The control system according to the present invention may be employed in track-laying vehicle power trains or transmissions of the type shown in US. Pat. No. 3,373,636 issued Mar. 19, 1968, to Livezey et al. and entitled VEHICLE TRANSMISSION INCLUD- ING STEERING BY DRIVING. The control system includes an upstream and a downstream main pressure regulator valve, the former regulating pressure at a value modulated according to both drive range and torque converter operation and used primarily for drive range engagement and converter lockup and the latter regulating pressure at an unmodulated value used primarily for directional drive engagement, control functions and as a source for control pressures. Two fluid velocity governors are provided, one producing a governor pressure (G1) proportional to converter turbine and power train output speed and the other producing a governor pressure (G2) which is zero throughout the lowest drive range and proportional to range unit and power train output speed in all of the higher drive ranges. A pair of throttle pressure regulator valves provide three control pressures, two of these control pressures (T and TV) derived by one valve from the unmodulated main pressure and the remaining control pressure (range TV) derived by the other valve from the unmodulated main pressure and TV pressure. The TV pressure is proportional to engine throttle opening, T pressure is the upper portion of the TV pressure range, and range TV pressure has a predetermined minimum value and is otherwise equivalent to TV pressure. A lockup valve under the control of implementing Gl pressure and inhibiting T and TV pressure determines converter lockup with a flow valve normally interrupting lockup during range shifting and a flow valve modulator valve under the control of TV pressure overriding the normal flow valve operation to permit maintainance of lockup with G1 pressure during range downshifting below a predetermined TV pressure or part engine throttle opening. A neutral shift valve under the control of a manually controlled solenoid valve determines the delivery of the modulated main pressure to series arranged range shift valves for drive range engagement.

The range shift valves operate to automatically shift between the drive ranges under the control of an upshift bias by G1 pressure for the lowest upshift, an upshift bias by G2 pressure for the higher upshifts, an upshift inhibiting bias by range TV pressure and a downstream bias by T pressure. The range shift valves under the control of manually controlled solenoid valves provide for manual range selection. For manual range selection, a manual signal valve under the control of manually controlled solenoid valves substitutes unmodulated main pressure for the T pressure downshift bias on the proper range shift valves to provide automatic downshifting from any higher drive range through any intermediate drive range to the manually selected drive range. This automatic downshifting with manual drive range selection is controlled to occur at a vehicle speed suitable for each lower drive range as determined by governor pressure bias, upshifts by manual selection occurring immediately.

A forward and reverse shift valve under the control of manually controlled solenoid valves determines the delivery of unmodulated main pressure for directional drive engagement in the selection being between forward and reverse drive. A forward and reverse inhibitor valve under the control of G2 pressure permits shifts between forward and reverse in the lowest drive range and prevents such shifting in all of the higher drive ranges. A sequence valve under the control of the operation of the forward and reverse shift valve effects disengagement of the drive to the load during a directional change in the lowest drive range to permit engagement of the directional drive under no-load conditions. An automatic shift inhibitor valve under the control of a steer signal pressure from the steer control inhibits automatic shifting during steering operation. There is also provided in the control system a converter pressure regulator valve which limits pressure to the torque converter, this pressure being modulated in accordance with converter operation, and an air valve which controls delivery of fluid to hydrodynamic and hydromechanical output brakes.

All of the solenoid valves are controlled by the operator from a selector box with a forward and reverse shift lever controlling solenoid valve operation for directional change and the remaining solenoid valves controlled by a manual and automatic shift lever for both manual drive selection and automatic range shifting. The solenoid valves are connected in the control system such that when they are all de-energized, the control system is conditioned for automatic range shifting in either drive direction, the forward and reverse shift valve being mechanically detented in each of its two drive determining positions. For automatic shifting operation, the forward and reverse shift lever is controlled by the operator to select the drive direction desired by energization of the proper direction control solenoid valve while the manual and automatic shift lever is operated to de-energize the remaining solenoid valves. Manual drive range selection is made by operating the manual and automatic shift lever to energize the proper solenoid valves to establish the desired drive range while the forward and reverse lever is operated to determine drive direction. Thus, with this arrangement and in the event there is an interruption in the electrical power while operating with manual drive selection, the control system will be automatically conditioned for automatic range shifting in the direction previously determined so that range shifting remains available.

The steer bias of the power train is effected by a converter pump driven hydrostatic unit, hydrostatic pump displacement being controlled by steer controls in the control system to control the steer bias. A manually controlled steer valve controls the delivery of a control pressure to vary hydrostatic pump displacement, the steer valve providing pump displacement in proportion to manual steer input. A centering and steer signal device accurately positions the steer valve for zero pump displacement and thus no steer bias when a steer is not being demanded and supplies the steer signal pressure to the automatic shift inhibitor valve for inhibiting automatic shifting during steering operation. A control pressure regulator valve always responsive to hydrostatic pump output pressure modulates the control pressure controlling pump displacement so that it increases with increasing hydrostatic pump output pressure and thus steer effort. An overload stroke limiter valve under the control of the pressure differential across the hydrostatic pump overrides steer control to prevent steer bias which would overload the hydrostatic pump. A relief valve is always connected to limit hydrostatic pump output pressure. The relief valve is under the control of a control pressure from a relief valve modulator valve which is controlled by range TV pressure and G2 pressure. In the lowest drive range the relief valve modulator valve control pressure to the relief valve controls maximum hydrostatic pump output pressure in accordance with range TV pressure to prevent pump overload and control pump power absorption to prevent engine stall. In all of the higher drive ranges the maximum hydrostatic pump output pressure in addition to the throttle pressure control is caused to decrease with increasing G2 pressure to prevent overloading the hydrostatic pump during demanded high speed turns.

An object of the present invention is to provide a new and improved power train control system.

Another object is to provide a new and improved power train control system providing both manual and automatic shifting.

Another object is to provide a power train control system having both a manual shift control and an automatic shift control wherein the automatic shift control remains available on discontinuance of power to the manual control.

Another object is to provide in a power train control system a torque converter lockup control for interrupting lockup during range shifting while holding lockup from zero to part engine throttle at low vehicle speeds.

Another object is to provide in a power train control system a sequence control to disengage a range drive on a directional change to permit directional drive engagement under no-load conditions.

Another object is to provide in a power train control system a manual shift control with automatic downshifting according to vehicle speed to a selected lower drive range.

Another object is to provide in a power train control system a directional drive inhibitor inhibiting directional changes in the power trains high drive ranges. i

Another object is to provide in a power train range and steer control system a shift inhibitor inhibiting automatic shifting during steering operation.

Another object is to provide in a power train control system an unmodulated main pressure source for directional drive engagement, control functions and control pressures and a modulated main pressure source for drive range engagement and converter lockup.

Another object is to provide in a power train control system multiple throttle pressures for different control functions including converter lockup range shifting and hydrostatic pressure relief.

Another object is to provide in a hydrostatic steer control of a power train control system a control pressure regulator modulating control pressure for steer bias according to hydrostatic pump output pressure.

Another object is to provide in a hydrostatic steer control of a power train control system an overload stroke limiter limiting hydrostatic pump displacement in accordance with differential pressure across the hydrostatic pump.

Another object is to provide in a hydrostatic steer control of a power train control system a maximum hydrostatic pump output pressure relief in accordance with engine throttle opening and vehicle speed.

Another object is to provide in a power train control system electrically actuated manual drive selection and automatic drive selection independent of electrical power.

Another object is to provide in a power train control system an electrically actuated manual range selection and directional drive and a fluid pressure actuated automatic range control automatically actuated on discontinuance of electrical power for manual selection while directional drive selection is maintained.

These and other objects of the present invention will be more apparent from the following description and drawings in which:

The power train and control system are shown schematically in FIGS. 2a, 2b, 2c, 2d and 2e, when arranged as indicated by FIG. 1.

FIG. 3 is a view taken on the line 3-3 in FIG. 2d.

F IG. 4 is a perspective view with parts broken away of the operators control in the power train control system.

FIG. 5 shows theschedule of power train operation.

POWER TRAIN ARRANGEMENT The invention is illustrated in an arrangement controlling a track-laying vehicle power train which is of the type shown in detail in the Livezey et al. U.S. Pat. No. 3,373,636 and is capable of providing multiple speed or drive range and hydrostatic steering operation in forward and reverse. The power train as shown in FIGS. 2a and 2d receives input from a prime mover 210 such as a piston engine and generally comprises a hydrodynamic torque converter 211, a forward and reverse drive unit 212, a three-speed planetary gear range unit 213, a left steer unit 214, a right steer unit 216, a differential unit 218, and a hydrostatic pump and motor steer unit 219 for controlling differential unit 218, all housed in a housing 222. These components are connected in the power train arrangement to provide four speed or drive ranges in forward and reverse and hydrostatically controlled steering.

In the power train arrangement, the engine 210 is connected to drive the power trains input shaft 224 which is connected by the converters rotary housing 226 to pump blading 228 (P). The pump blading 228 exits fluid to turbine blading 229 (T) which is connected by hub 231 to converter output shaft 232. Fluid is redirected to pump blading 228 by stator blading 234 .(S) which is grounded to the power train housing for reaction by one-way brake 236. A converter lockup clutch 238 connected between converter housing 226 and hub 231, when engaged, provides direct mechanical drive between power train input shaft 224 and converter output shaft 232.

The converter output shaft 232 provides input to both the range unit 213 and the differential unit 218 via the forward and reverse drive unit 212, the range unit 213 providing one input to each of the steer units 214 and 216 and the differential unit 218 providing another input to each of the steer units. In the drive to forward and reverse drive unit 212, the converter output shaft 232 is connected at its left end to a gear 239 meshing with an idler gear 240. Idler gear 240 meshes with a gear 241 which latter gear is connected to a shaft 242. Shaft 242 is connected to clutch drum 244 of the forward and reverse drive unit 212. Drum 244 is connectible through either a forward or reverse drive to both the range unit 213 and differential unit 218. For the forward drive units 213 and 218, unit 212 has a forward drive clutch 246 which, when engaged, connects drum 244 to a gear 247 geared to drive an annular gear 248. In this gear drive, gear 247 meshes as illustrated schematically by the dashed line with an idler gear 245 which latter gear meshes with the gear 248. Gear 248 is connected to a sleeve shaft 249 which is the input shaft of range unit 213. Gear 247 also meshes with an annular gear 250 which is connected to drum 251 of the differential unit 218, unit 218 being described in more detail later. Thus, in the forward drive gear train provided and with the forward drive clutch 246 engaged, shaft 242 drives the range unit input shaft 249 in the same direction and the differential drum 251 in the opposite direction.

For the reverse drive to the units 213 and 218, a reverse drive clutch 252 in unit 212 is engaged to connect drum 244 to an annular gear 254 freely received on shaft 242. Gear 254 meshes with an idler gear 256 which meshes with an annular gear 257. Gear 257 is connected by the differential drum 251 to the gear 250 at the other end of the drum. The drive is then from gear 250 via gears 247, 245 and 248 to the range unit input shaft 249. Thus, with the reverse drive clutch 252 engaged, shaft 242 drives the range unit input shaft 249 in the opposite direction and the differential drum 251 in the same direction.

In the range unit 213, its input shaft 249 is connected to both the annular sun gear 258 of a low ratio planetary gear set 259 and the annular sun gear 261 of an intermediate ratio planetary gear set 262. The sun gear 258 meshes with pinions 264 journaled on an output carrier 266. Ring gear 268 of the low ratio gear set meshes with pinions 264, is connected to carrier 269 of the intermediate ratio gear set, and may be held by a low brake 271 to provide a low ratio drive to output carrier 266. The sun gear 261 of the intermediate ratio gear set meshes with pinions 272 journaled on carrier 269. Ring gear 274 of the intermediate ratio gear set meshes with pinions 272 and may be held by an intermediate brake 276 to provide higher speed and intermediate ratio drive to output carrier 266. A high clutch 278, when engaged, connects the range unit input shaft 249 to the intermediate carrier 269 and connected low ring gear 268 to lock the low ratio gear set 259 to provide direct drive between the range unit's input and output.

The range unit output carrier 266 is connected by a hub 279 to range unit output shaft 280 which extends freely through sleeve shaft 249, shaft 280 serving as both the range units output shaft and the steer unit input shaft. Shaft 280 is connected at its left end to ring gear 281 of a planetary gear set 282 in left steer unit 214 and at its right end to ring gear 284 of a planetary gear set 286 in right steer unit 216, gear sets 282 and 286 having equal speed ratios.

On the left side, the ring gear 281 of gear set 282 meshes with pinions 287 journaled on an output carrier 288. An annular sun gear 290 freely received on shaft 280 meshes with pinions 287 and is connected to be controlled by the differential unit 218 as described in more detail later. A drum 291 connects carrier 288 to the power train s left output shaft 292 which shaft is for powering the vehicles left track. A mechanical brake 299 and a hydrodynamic brake 300 are both connected to brake the power train s left output shaft 292.

On the right side, the ring gear 284 of gear set 286 meshes with pinions 301 journaled on an output carrier 302. A drum 303 connects carrier 302 to the power train s right output shaft 304 for powering the vehicles right track. An annular sungear 306 freely received on shaft 280 meshes with pinions 301 and is connected to be controlled by the differential unit 218. A mechanical brake 316 and a hydrodynamic brake 317 are both connected to brake the power trains right output shaft 304.

A low low brake 318, when engaged, is connected by the hub 279 to hold shaft 280 and the connected ring gears 281 and 284 of the steer units. This enables the sun gears 290 and 306 of the steer units to produce drive in the steer units without output from the range unit and at the lowest available ratio as described in more detail later.

Describing the hydrostatically controlled differential unit 218, the sun gears 290 and 306 of the steer units are continuously connected by equal speed ratio and direction reversing gear trains to output carriers 322 and 324 of equal speed ratio planetary gear sets 326 and 328, respectively, provided in unit 218. The left gear train comprises an annular gear 325 which is connected to sun gear 200 of the left steer unit and meshes with an annular gear 323. Gear 323 is connected by a sleeve shaft 327 to the left output carrier 322 of unit 218. The right gear train similarly comprises an annular gear 328 which is connected to sun gear 306 of the right steer unit and meshes with an annular gear 329. Gear 329 is connected by a sleeve shaft 330 to the right output carrier 324 of unit 218. The ring gears 331 and 332 of gear sets 326 and 328 are both connected to the drum 251, driven by the forward and reverse drive unit 212. Pinions 334 journaled on the left output carrier 322 mesh with the ring gear 331 and a sun gear 336. Similarly, pinions 338 journaled on the right output carrier 324 mesh with the ring gear 332 and an annular sun gear 339. The sun gears 336 and 339 mesh with meshing differential pinions 341 and 342, respectively. The differential pinions 341 and 342 are journaled on spindles attached to a differential carrier 344 which is continuously grounded to the power train housing by a shaft 346 which extends through annular sun gear 339.

Hydrostatic control of differential unit 218 is provided by the hydrostatic unit 219 shown in FIG. 2d operating on sun gear 336 of differential unit 218 which sun gear is connected by a shaft 349 to a gear 351, shaft 349 extending through sleeve shaft 327 to make the connection. Gear 351 meshes with a gear 352 which latter gear is connected by a motor output sleeve shaft 354 to the hydrostatic motor 356. The hydrostatic pump 358 is input driven through a gear train which has an annular gear 359 connected to the converter housing 226 and meshing with an idler gear 361. Gear 361 meshes with an annular gear 365 which is connected by a pump input sleeve shaft 367 to the hydrostatic pump 358, the input shaft 242 of the forward and reverse drive unit 212 extending freely through both shafts 367 and 354. Preferably, the hydrostatic pump 358 and hydrostatic motor 356 are axially aligned as one unit and located between the gears 365 and 352 with their central axis coinciding with that of the shaft 242 which then extends freely through the hydrostatic pump and motor steer unit. The pump 358 has a variable displacement and the motor 356 has a fixed displacement and the hydrostatic unit is conditionable to hold motor output shaft 354 and to drive the motor output shaft in either direction at infinitely variable speed;

The drive producing clutches and brakes are conventional friction drive establishing devices of the friction plate type each having a suitable fluid motor which is operated by fluid pressure to effect engagement of the device. Each of these devices also has suitable retraction spring means, not shown, that operate on exhaust of the fluid pressure to effect disengagement of the device. The output mechanical brakes 299 and 316 have conventional structure and are operated simultaneously by conventional linkage which includes a rotary or otherwise movable member such as shaft 370 shown in FIG. 2c which shaft turns during engagement and disengagement of these brakes.

OPERATION OF POWER TRAIN ARRANGEMENT The power train may be operated to provide four speed or drive ranges in forward and reverse and hydrostatically controlled steering. The first 1 or low low drive range which is considered the lowest drive range and provides the greatest torque multiplication is established by engaging the forward drive clutch 246 in the case of forward drive and the low low brake 318 and conditioning the hydrostatic steer unit 219 to hold the motor output shaft 354 and thus the controlled sun gear 336 in differential unit 218, all other drive establishing devices being disengaged. Since the carrier 344 in the differential unit is grounded and the sun gear 336 is held by the hydrostatic steer unit, rotation of the other sun gear 339 is also prevented. With ring gears 331 and 332 of the differential unit being driven at the same speed and in the same direction by converter 21] through the forward drive clutch 246, the differential output carriers 322 and 324 are driven in the same direction at the same speed by locked drives. Thus, the sun gears 290 and 306 of steer units 214 and 216 are driven in the same direction which is forward and at the same speed while both of the ring gears 281 and 284 of the steer units are held by the low low brake 318. Therefore, the gear sets 282 and 286 in the steer units act as reduction gear sets with the locked input drives thus provided to drive the power train output shafts 292 and 304 in the forward direction at the same speed. When the speed of the converter turbine 229 reaches a desired value the lockup clutch 238 is engaged to provide mechanical drive instead of the hydraulic drive through the converter.

In the differential unit 218, rotation of sun gear 336 in either direction with the infinitely variable speed drive made available by the hydrostatic steer unit 219 results in opposite rotation of sun gear 339 at the same speed. Thus, the output carriers 322 and 324 and their gear train connected sun gears 290 and 306 of the steer units are driven at equal differential speeds measured from their same base speed with sun gear 336 held since the speed of these carriers is determined by the combination of the equal speed ratio drive to the connected ring gears 331 and 332 and the equal speed opposite directional drive to the sun gears 336 and 339.

Thus, for steering in the first forward drive range the hydrostatic steer unit 219 is conditioned so that instead of continuing to hold the differential units sun gear 336, it then drives the controlled sun gear 336 in either direction depending on the direction of vehicle turn desired. Then, with sun gear 336 rotating in one direction, the other differential sun gear 339 is caused to rotate in the opposite direction at the same speed. The combined differential action in the gear sets 326 and 328 that results causes, as for example when sun gear 336 is driven in the same direction as the ring gears 331 and 332, the carrier 322 to speed up by the same amount that the carrier 324 is being slowed down. In this manner the sun gears 290 and 302 in the steer units are differentially driven in the same direction or in opposite directions with locked differential drives, recognizing that the left sun gear 290, for example, will be speeded up by the same amount that the speed of the right sun gear 306 is diminished to thereby establish the differential steering. The steering radius is thus put under positive control and made infinitely variable by units 218 and 219 from straight ahead drive in the first drive range down to the minimum radius possible with gearing provided.

The three higher drive ranges (2, 3, 4) in the forward direction are established by driving the connected ring gears 281 and 284 in the steer units forward at different speeds with the forward clutch 246 remaining engaged, the sun gear 336 of the differential gear unit 218 held by the hydrostatic steer unit 219 and selective conditioning of the range unit 213 to provide its low ratio drive (low brake 271 engaged), intermediate ratio drive (intermediate brake 376 engaged), and high ratio drive (high clutch 278 engaged) in that order. In these three higher drive ranges, the steer units then act as power combining and speed differential devices receiving power from both the range unit 213 and the differential unit 218. Hydrostatically controlled differential steering is available in these higher ranges by control of the hydrostatic steer unit 219 to provide locked differential drive as described in the first drive range, recognizing that-the speed added to one of the steer unit sun gears will be equal to the speed subtracted from the opposite steer unit sun gear while the connected ring gears of the steer units continue to rotate forwardly with their drive from range unit 213. Thus, the output speed in one steer unit is increased by the amount the output speed of the other steer gear unit is diminished to provide the differential steering. Again, the steer radius is under positive control and infinitely variable in the second, third and fourth forward drive ranges from straight ahead down to the minimum radius possible with the gearing provided.

Since the forward and reverse drive unit 212 provides the input to both the range unit 213 and differential unit 218, the same drive ranges and hydrostatically controlled differential steering provided in forward as described above, are also available in reverse by simply disengaging the forward drive clutch 246, engaging the reverse drive clutch 252 and operating range unit 213 and hydrostatic steer unit 219 as before.

For neutral, either the forward or reverse drive I clutch is preferably engaged, all other drive establishing devices are disengaged, the sun gear 336 of the differential unit 218 is held by the hydrostatic steer unit 219 and there is no output drive to the power train output shafts 292 and 304. Steering in neutral is provided by controlling the hydrostatic steer unit 219 to drive the sun gear 336 in the differential unit 218 in either direction dependent on the direction of vehicle turn desired. This causes the opposite sun gear 339 of the differential gear unit to rotate in the opposite direction at the same speed and since the drum 251 is acted on by opposed gear forces, the connected ring gears 331 and 332, through free, provide reaction in their gear sets. Thus, the output carriers 322 and 324 of the differential unit are caused to rotate at equal speeds in opposite directions. Because the sun gears 290 and 306 of the steer units are being driven in opposite directions and at the same speed by the free differential drives provided by unit 218, the connected ring gears 281 and 284 of the steer units, though free, provide reaction resulting in the power train output shafts 292 and 304 being driven at equal speeds in opposite directions to produce pivot steering.

CONTROL SYSTEM The control system for this power train arrangement and according to the present invention provides for both automatic and manual selection of the four drive ranges in both forward and reverse and steering control in all drive ranges and neutral. Other functions of the control system include lubrication, cooling, charging of the torque converter, and charging of the hydrodynamic brakes.

FLUID SUPPLY The fluid such as oil used in all of the control functions is suppliedby four gear-type positive displacement pumps shown in FIG. which draw from a reservoir 400 to which the fluid exhaust from all parts of the system is returned. Fluid which tends to accumulate in certain locations in the power train housing 222 is scavenged by one or more input driven scavenge pumps, not shown, which remove this excess fluid and return it to the reservoir.

The pump 402, which is called the hydrostatic supercharge-converter pump, is drivingly connected to the power train input shaft 224 so that it is continuously driven to supply fluid when the engine is operating. This pump supplies both the hydrostatic steer portion and the torque converter portion of the system.

The pump which is called the coolant pump, is drivingly connected to the converter turbine 229 so that it is driven to supply fluid when the converter turbine is being driven. The fluid supplied by this pump is delivered to charge the hydrodynamic output brakes 300 and 317 with this same fluid then being used to flood the friction plates of the mechanical output brakes 299 and 316 to cool them during their engagement.

The pump 406, which is calledthe main pressure input pump, is drivingly connected to the power train input shaft 224 so that it is continuously driven to supply fluid when the engine is operating. The fluid supplied by this pump furnishes the main fluid supply to the shift control portion of the control system which controls the shifting of the power train and also delivers fluid to lubricate various parts of the power train.

The pump 408, which is called the main pressure output pump, is drivingly connected to one of the power train output shafts, output shaft 292 for example, so that it is driven to supply fluid only when the vehicle is moving forwardly. The fluid supplied by this pump supplements the fluid supply from the main pressure input pump 406 during forward drive operation and is the only source of main pressure supply when the main pressure input pump is not operating.

HYDROSTATIC SUPERCHARGE PRESSURE REGULATOR VALVE The hydrostatic supercharge-converter pump 402 draws fluid from the reservoir 400 via intake line 410 and delivers this fluid to a hydrostatic supercharge-converter supply line 412. Line 412 as shown in FIG. 2a is connected to a chamber 414 in one end ofthe valve body of a hydrostatic supercharge pressure regulator valve 416 which in addition to providing a regulated low pressure source for the hydrostatic portion of the control system admits fluid to the torque converter 211. Regulator valve 416 has a regulator valve element 418 with a land a located in bore 420 of a sleeve 422 secured in the valve body. A valve stem 424 bottomed on a retaining ring 426 has a land 0 located in a blind bore 428 in the lower end of regulator valve element 418 to provide a clamping chamber 430. Chamber 430 is continuously connected by an orifice 432 and an elongated annular channel 433 in regulator valve element 418 to the control systems main line which has fluid at main pressure as described in more detail later.

The force of a spring 434 arranged between the regulator valve element 418 and the base of the valve stem 424 plus the main pressure in damping chamber 430 urge the regulator valve element 418 upward toward the closed position shown, the closed position determined by shoulder 436 of valve element 418 abutting collar 438 of sleeve 422. The regulator valve element 418 in its closed position closes a converter-in line 440 from the hydrostatic supercharge-converter supply line 412. These forces are opposed by the pressure from line 412 acting on the full upper end area of land a of regulator valve element 418 which urges the regulator valve element downward toward an open position connecting line 412 to the converter-in line 440 through porting 441 in sleeve 422. The spring bias of the regulating spring 434 plus the pressure bias in chamber 430 provide for regulation of pressure (hydrostatic supercharge pressure) in line 412 to the desired value with the overage delivered to the converter-in line 440. The damping chamber 430 with its restricted connectionby orifice 432 to the control systems main line prevents the shoulder 436 from battering the collar 438 during the pressure regulation.

CONVERTER PRESSURE REGULATOR VALVE The pressure of the fluid admitted by the hydrostatic supercharge pressure regulator valve 416 to the converter-in line 440 is reduced to either one of the two lower regulated pressures by a converter pressure regulator valve 442 shown in FIG. 2a. The high regulated pressure provided by the converter pressure regulator valve 442 is for normal converter operation and the low regulated pressure is for lockup operation with the lockup clutch 238 engaged. The converter-in line 440 is connected to a chamber 444 in the upper end of the valve body of regulator valve 442 which has a regulator valve element 446 guided by a rod 448 extending through central bore 450 in the valve element. The rod 448 is secured at its lower end to a plug 452 located in bore 454 of the valve body, plug 452 in cooperation with bore 454 providing a chamber 456. A spring 458 arranged between the regulator valve element 446 and plug 452 urges the regulator valve element upward toward the closed position shown. The regulator valve element 446 in its closed position closes the chamber 444 and connected converter-in line 440 from an exhaust 460. The closing force is opposed by pressure from the converter-in line 440 acting in chamber 444 on the regulator valve element 446, this pressure urging the regulator valve element downward toward an open position connecting the chamber 444 to exhaust 460. The low regulated pressure is provided when the chamber 456 is exhausted and the plug 452 is bottomed so that the normal bias of regulating spring 458 determines the opening and closing of the valve.

The high regulated pressure by converter pressure regulator valve 442 is provided when a pressure signal is delivered to the chamber 456 from the lockup shift control portion of the control system as described in more detail later. The pressure delivered to chamber 456 raises the plug 452 upward to the position shown in which it abuts with a stop ring 461 thereby increasing the bias applied by spring 458 to the regulator valve element 446 to effect the high pressure regulation. An elongated external annular channel 462 in the plug 452 is supplied with fluid from the control systems main line described later so that the plug floats on a constant film of fluid allowing it to move readily between its low and high pressure positions.

The fluid at pressure regulated by the converter pressure regulator valve 442 is delivered by the converterin line 440 to the torque converter 211. The fluid leaves the converter by a converter-out line 464 which passes it through a cooler 466 located externally of the power train housing prior to returning it to the reservoir 400, the restriction to flow through the converterout line 464 and cooler 466 maintaining pressure at the converter outlet.

The capacity of the hydrostatic supercharge-converter pump 402 is sufficient to meet the requirements of both the hydrostatic portion of the control system and the torque converter during all their operating conditions, the high charging pressure for converter operation maintaining the converter filled with fluid while effecting sufficient flow to carry away heat for dissipation in the cooler. During lockup operation, the converter requires a smaller volume of fluid which is effected by the low regulated pressure provided by the converter pressure regulator valve 442.

HYDRODYNAMIC BRAKES The coolant pump 404 is operable to draw fluid from the reservoir 400 via an intake line 468 through a check valve 470 and deliver the fluid to a coolant line 472 as shown in FIG. 20. Coolant line 472 is connected to cavities 474 and 476 of the hydrodynamic brakes 300 and 317, respectively, as shown in FIG. 20. With rotors 478 and 480 of the hydrodynamic brakes 300 and 317, respectively, rotating through their fluid-filled cavity, there is provided hydrodynamic braking of the power train output shafts. When pump 404 is operating the fluid continuously passes through the cavities 474 and 476 and is directed by mechanical brake coolant lines 482 and 484 to cool the friction plates of the mechanical output brakes 299 and 316, respectively.

AIR VALVE Control over delivery of fluid by the coolant pump 404 to the hydrodynamic and mechanical output brakes is provided by an air valve 486 shown in FIG. 2c. Air valve 486 has a valve element 438 which in the open position shown opens chamber 490 in the valve body via a port 491 to an air line 492, chamber 490 being open to atmosphere. Air line 492 is connected to the intake side of the coolant pump 404 upstream of check valve 470. Thus, when the coolant pump is being driven with the air valve 486 open, the check valve 470 closes and the coolant pump is air bled and delivers only air to the cavities of the hydrodynamic and mechanical output brakes thereby belljarring these cavities to force any fluid therein back to the reservoir. When the air valve element 488 is moved to a closed position closing port 491 and thus closing the air line 492 to the atmospheric chamber 490, air is prevented from entering the intake side of the coolant pump which then operates to draw fluid through the check valve 470 for delivery to the brakes.

The opening and closing of the air valve 486 is under the control of the mechanical linkage which operates the mechanical output brakes 299 and 316. The valve element 488 is secured to the upper end of a right-angle arm 494 which is pivoted at its bend on a pivot pin 496 secured in the valve body. The lower end of arm 494 has an aperture through which a control rod 498 extends, the rod being mounted for reciprocal movement in stepped bore 499 in the valve body. When the mechanical output brakes are disengaged, shaft 370 of their linkage is in the angular position shown in FIG. 2c. An arm 500 splined to shaft 370 engages the projecting left end of control rod 498 so that while the mechanical output brakes are disengaged, a spring 502 mounted in a bore 503 in the valve body and between a screw plug 504 and the lower end of arm 494 holds the latter against a collar 506 on the control rod 498. This positions and holds the valve element 488 in its open position so that the coolant pump 404 is air bled when the mechanical output brakes are disengaged.- When the mechanical output brakes are engaged by the operator, shaft 370 is pivoted counterclockwise as shown by the directional arrow. This swings arm 500 counterclockwise and the spring 502 forcesthe control rod 498 to follow arm 500 while forcing the lower end of arm 494 to follow the collar 506 and swing valve element 488 to its closed position, the collar 506 abutting shoulder 501 in bore 499 to limit the leftward movement of the control rod. With the air valve 486 closed the coolant pump 404 is no longer air bled and then delivers fluid to the brakes as previously described. The motion of the mechanical linkage operating the mechanical brakes is such that the air valve 486 closes prior to initial engagement of the mechanical output brakes so that the hydrodynamic brakes are put in operation first to retard the vehicle.

MAIN PRESSURE REGULATOR VALVE I The main pressure input pump 406 draws fluid from the reservoir 400 via intake line 508 and delivers this fluid to a main line 510. The main pressure output pump 408 draws fluid from the reservoir via an intake line 512 and delivers this fluid through a check valve 514 to main line'SlO. The fluid delivered to main line 510 from these pumps is passed through a filter 516 prior toflowing to all downstream portions of the control system.

The main pressure supply for the shift control portion of the control system is regulated in main line 510 by a main pressure regulator valve 518 shown in FIG. 2c, the valve delivering the excess fluid to lubricate parts of the power train. The main pressure regulator valve 518 has a regulator valve element 520 having lands a and b of equal diameter located in bore 522 of the valve body. Regulator valve element 520 is normally biased to the right to the position shown by two springs 524 and 526. The spring 524 is located between left end wall 527 of the valve body and a shoulder 530 on the regulator valve element 520. The spring 526 is located in a blind bore 532 in the left end of the regulator valve element 520 and between the regulator valve element and a plug 536 which is bottomed at its left end on the valve body wall 527, the regulator valve element being movable with respect to plug 536. The main line 510 is always connected to the bore 522 in the space between lands a and b. This space is always connected to a passage 538 in regulator valve element 520 having a spring loaded ball check valve 540 therein permitting fluid flow from the main line 510 to the bore 522 between land b and right end wall 542 of the valve body. The fluid admittedto the right end of the valve bore 522 acts on the exposed end area of land b so that the valve regulates the pressure in main line 510 with the normal action of the regulating springs 524'and 526. The check valve 540 in cooperation with an orifice 544 through land b damps the action of the regulator valve. The fluid overage resulting from the regulating action upon leftward regulator valve'element movement to maintain the main line pressure is delivered to a lubrication line 546.

The' action of regulating springs 524 and 526 with no assist establishes a low main pressure in main line 510. This low main pressure is used when the control system is controlling third and fourth drive range operations in either forward or reverse and neutral. When the power train is operating in the first and second drive ranges in either forward or reverse, the regulating springs are assisted by fluid pressure to boost main line pressure to a higher regulated value. The regulated high main pressure is provided by directing a signal pressure indicating first and second drive range operation .to a port 548 in the valve body which is continuously connected by a channel 550 in land a of the regulator valve element 520 and a passage 552 to chamber 554 in the left end of the regulator valve element, such chamber being provided by the bore 532 and plug 536. The fluid pressure thus delivered to the chamber 554 acts leftward on the bottomed plug 536 and rightward on the regulator valve element 520 thereby assisting the regulating springs and boosting the regulated pressure in main line 510 to the higher value.

The main pressure, when it is at either its low or high value, is decreased during converter lockup operation. This is permissible since lower torque at higher rotating speeds is being transmitted through the power train. To this end, the regulator valve element 520 has a reduced diameter portion 556 which extends through an aperture in the end wall 542 of the valve body into a chamber 558. When fluid pressure indicating lockup operation is delivered to the chamber 558 as described in more detail later, such pressure acts leftward on the regulator valve element 520 to decrease main line pressure.

The main line 510 is connected to the damping chamber 430 of the hydrostatic supercharge pressure regulator valve 416 and channel 462 of the converter FORWARD AND REVERSE MAIN PRESSURE REGULATOR VALVE Main line 510 is also connected to a forward and reverse main pressure regulator valve 560 which is shown in FIG. 20. Valve 560 has a regulator valve element 561 with lands a and b of equal diameter located in bore 562 of the-valve body. The valve element 561 is normally biased to the open position shown by spring 564. A forward and reverse main line 566 is always connected to a passage 567 in the valve element having a spring loaded ball check valve 568 therein permitting fluid flow from the forward and reverse main line 566 to the right end of the valve bore 562. The fluid in the right end of the valve bore acts leftward on the full end area of land b to close the connection to main line 510 so that the valve regulates the pressure in the forward and reverse main line 566 even though main pressure is subject to modulation which gives several pressure levels as previously described. The check valve 568 in cooperation with a small clearance between land b and the bore 562 damps the action of the regulator valve.

GOVERNORS 546 via orifice 571 shown in FIG. 20. This fluid impinges on the open end of a pitot tube 572 to provide in a G1 line 573 a governor pressure (G1 pressure) which is proportional toconverter turbine speed.

The other governor 574 called the G2 governor is also shown in FIG. 2a and has its annular trough 575 connected to the range unit output shaft 280. The trough 575 is maintained suitably filled with fluid from the lubrication line 546 via orifice 571 like the G1 governor 569. This fluid impinges on either open end of a double ended pitot tube 576 having a two way check valve between the open ends to provide in a G2 line 577 a governor pressure (G2 pressure) which is proportional to vehicle speed in second, third and fourth drive range operations in forward and reverse, the range unit output shaft 280 being stationary in the first drive range in forward and reverse.

PRIMARY THROTTLE PRESSURE REGULATOR VALVE AND SECONDARY THROTTLE PRESSURE REGULATOR VALVE Three pressures indicating engine torque demand and used primarily for control of various automatic operations in the control system are provided. These are T pressure, TV pressure and range TV pressure. The T and TV pressures are derived from forward and reverse main pressure in the line 566 by a primary throttle pressure regulator valve 580 (primary TV valve) and the range TV pressure is derived from forward and reverse main pressure in line 566 by a secondary throttle pressure regulator valve 582 (secondary TV valve), both of these valves being shown in FIG. 2c.

The primary TV valve 580 has a regulator valve element 584 having lands a and b of equal diameter located in a small diameter portion of a bore 586 in the valve body. The valve also has a control valve element 587 having lands a and b of equal diameter and larger in diameter than the lands of valve element 584 located in a large diameter portion of bore 586. A zero or closed throttle to full throttle regulating spring 589 and a detent spring 590 of shorter length are located between the two valve elements 584 and 587.

The positioning of the control valve element 587 is controlled by a throttle cam 591 which contacts the projecting right end of the control valve element 587 and is pivoted by pivot pin 592 on the valve body, the throttle cam 591 being connected by suitable linkage to the engine throttle control, not shown, which controls the throttling of the engine 210. When the engine throttle is closed or at zero throttle position, the cam 591 is against a stop 593 and the two valve elements 584 and 587 are positioned as shown with the outer spring 589 positioning the control valve element 587 against the cam 591. At the zero position of the control valve element 587 which corresponds to closed engine throttle, there is no spring loading on the regulator valve element 584 and its land a blocks the forward and reverse main line 566 so that a TV line 594 receives no pressure, TV line 594 being continuously connected to the space between lands a and b of the regulator valve element. As the engine throttle is opened, the cam 591 is pivoted clockwise moving the control valve element 587 leftward. This leftward movement causes the spring 589 to load the regulator valve element 584 and opens the forward and reverse main line 566 so that fluid is delivered between lands a and b of the regulator valve element to the TV line 594. The TV line 594 is always connected to a passage 595 in the regulator valve element 584 having a spring loaded ball check valve 596 therein permitting fluid flow from the TV line 594 to chamber 597 at the left end of the valve body. The fluid pressure in chamber 597 acts rightward on the full and area of land a so that the valve regulates to provide TV pressure in the TV line 594 according to the acting spring bias of regulating spring 589 with average being delivered to an exhaust 598. The TV line 594 is also connected to the chamber 597 through an orifice 600 so that the ball check valve 596 in cooperation with the orifice 600 clamps the regulating action of the valve. An exhaust 601 exhausts any leakage that otherwise might collect in bore 586 between valve elements 584 and 587.

Since movement of the valve element 587 is proportional to the engine throttle opening which is indicative of engine torque demand, the spring load thus provided on the regulator valve element 584 is also proportional to engine throttle opening and indicative of engine torque demand. Thus, the TV pressure produced in TV line 594 is proportional to engine throttle opening and increases with increasing throttle opening and torque demand.

The control valve element 587 at a point corresponding to full engine throttle opening and near the elements limit of leftward travel, percent for example, begins pressing the detent spring 590. Thus, leftward movement of control valve element 587 past 80 percent travel causes the detent spring 590 to load the regulator valve element 584 in addition to the spring bias of spring 589 while the linkage to the engine throttle passes through a detent. Thus, through detent past full engine throttle, TV pressure increases rapidly at an increased rate to its maximum.

The TV line 594 is always connected at bore 586 around the control valve element 587 and through the valve body as shown. The control valve element 587 at a point about midway through its maximum travel, 40 percent for example, connects the TV line 594 between the elements lands a and b to a T line 604 and -'throughout the remainder of leftward movement of the control valve element. The TV pressure delivered to the T line 604 provides the T pressure which is thusthe upper part of the range of TV pressure in TV line 594.

The secondary TV valve 582 has a regulator valve element 605 with equal diameter lands a and b located in a bore 606 of the valve body. A regulator spring 608 biases the regultor valve element 605 leftward to connect the forward and reverse main line 566 via the space between lands a and b to a range TV line 610 which is always connected to this space. This space is always connected to a passage 6 12 in the regulator valve element having a spring loaded ball check valve 614 therein permitting flow from the range TV line 610 to a chamber 616 at the left end of the valve body. The fluid pressure in chamber 616 acts on the full end area of land a to urge the regulator valve element 605 rightward against the spring bias. With rightward movement of regulator valve element 605, land a closes the connection to the forward and reverse main line 566 and opens the range TV line 610 between lands a and b to the TV line 594. The range TV line 610 is connected through an orifice 618 to chamber 616 so that the orifice and check valve 614 cooperatively provide for damping regulator valve element movement during pressure regulation. An orifice 619 exhausts any leakage that might otherwise collect in the right end of bore 606.

The secondary TV valve 582 regulates to provide minimum range TV pressure in range TV line 610 according to the bias of regulator spring 608 as long as overage can exhaust the the TV line 594, i.e. range TV pressure is greater than TV pressure. When TV pressure is equal to or greater than the minimum range TV pressure determined by the regulator spring 608, overage exhaust is prevented by TV pressure. TV pressure is then transmitted from the lockup TV line 594 to the range TV line 610 by what was before the regulator exhaust connection of the secondary TV valve 582. The TV pressure in the range TV line 610 is transmitted to chamber 616 where it acts to hold the regulator valve element 605 in what would normally be its exhaust position so that the TV pressure connection is maintained when TV pressure is equal to or greater than the minimum range TV pressure.

Thus, the minimum range TV pressure in line 610 is provided by regulating action of the secondary TV valve 582. Higher range TV pressure in line 610 is provided by TV pressure through the valve upon cessation of its regulating action when TV pressure is equal to or greater than the minimum range TV pressure.

FLOW VALVE The main line 510 is connected to a range main line 626 by a flow valve 628 shown in FIG. 2a. Flow valve 628 has a valve element 630 having lands a and b of equal diameter located in portion 632 of a stepped bore 633 in the valve body and a land c of larger diameter located in bore portion 634. Mainline 510 is connected to the left end of bore 633 to act rightward on the full end area of land a and is connected to the range main line 626 via an orifice 636 in the valve body. The range main line 626 is connected via an orifice 638 to the right end of bore 633 where it acts leftward on the full end area of the larger land 0.

When there is no flow from main line 510 to range main line 626 through orifice 636, the pressures on the opposite ends of the flow valve element 630 are equal and the pressure on the larger land c holds the valve in the no-flow position shown. In the no-flow position the valve element 630 connects the G1 line 573 between lands a and b to a Gl-lockup line 639 and land b blocks a GI-exhaust line 640 from the space between lands a and b.

When there is flow, which occurs during a range shift, the pressure drop which results at the orifice 636 reduces pressure in the range main line 626 and thus the pressure acting on the larger land 0. This pressure reduction is sufficient to cause the valve element 630 to move rightward to a lockup cutoff or flow position. Rapid rightward movement of the flow valve element 630 is permitted by a ball check valve 641 which unseats to 'permit flow from the right end of bore 633 to the range main line 626. In the lockup cutoff position, land a of valve element 630 blocks the G1 line 573 and the G1 lockup line 639 is connected between lands a and b to the G1 exhaust line 640.

After the range shift is made, pressure increases in the range main line 626 until the pressures at each side of the flow valve orifice 636 are again equal. When this occurs, the check valve 641 closes and fluid flows back into the right end of bore 633 through the orifice 638 which bypasses the check valve 641. The return flow through orifice 638 is slower than the flow through the check valve 641 and thus the leftward movement of the flow valve element 630 that results is slower than the rightward movement. An exhaust 642 connected at the step in bore 630 between lands b and c prevents hydraulic locking of valve element 630.

FLOW VALVE MODULATOR VALVE A flow valve modulator valve 646 shown in FIG. 2e provides for normal operation of the flow valve 628 to control connection of the Gl-lockup line 639 between the G1 line 573 and exhaust above a predetermined part engine throttle opening on a range shift and bypasses the noral action of the flow valve 628 below this engine throttle opening so that the G1 line 573 and Gl-lockup line 639 remain connected on a range shift. The flow valve modulator valve 646 has a valve element 648 having lands a and b locatedin a bore 650 of the valve body. The valve element 648 is biased upward by a spring 652 to a bypass position connecting the G1 line 573 between lands a and b to the Gl-exhaust line 640. Thus, when the flow valve 628 is in its lockup cutoff position and the flow valve modulator valve 646 is in its bypass position, the G1 line 573 remains connected to the Gl-lockup line 639.

The TV line 594 is connected to the upper end of bore 650 so that TV pressure acts downward on the full end area of land a of the valve element 648 against the spring bias. The TV pressure above a predetermined part engine throttle opening prevails over the spring bias and moves the valve element 648 to the exhaust position shown connecting the G1 exhaust line 640 between lands a and b to an exhaust 653 while land 0 blocks the G1 line 573. Thus, when the flow valve 638 is in its lockup cutoff position and the flow valve modulator valve 646 is in its exhaust position the Gl-lockup line 639 is disconnected from the G1 line 573 and connected to exhaust 653.

LOCKUP VALVE A lockup valve 654 shown in FIG. 2c controls the delivery of main pressure in main line 510 to a lockup clutch motor 656 shown in FIG. 2a which operates the converter lockup clutch 238. The lockup valve 654 has a valve element 658 having lands a, b and c of equal diameter and a G1 plug 660 of larger diameter located in a stepped bore 662 in the valve body. A spring 666 located in the left end of the bore urges the shift valve element 658 and the G1 plug 660 to the position shown which is the release position. In this position a lockup clutch line 668 connected to both the lockup clutch motor 656 and the chamber 558 of the main pressure regulator valve 518 is exhausted between lands b and c to exhaust 670. Thus, the lockup clutch 238 is released and main pressure is regulated at its low value by the main pressure regulator valve 518. In addition, the lockup valve 654 when in the release position connects main line 510 between the lands a and b to a converter signal line 672 which is connected to chamber 456 of the converter pressure regulator valve 442. Thus, converter-in pressure is regulated at its high value by the converter pressure regulator valve 442 for normal converter operation with the lockup clutch released.

The lockup valve element 658 is biased to the left to an apply or lockup position by G1 pressure under the control of the flow valve 628 and the flow valve modulator valve 646. This is provided by connection of the Gl-lockup line 639 to the bore 662 between the G1 governor plug 660 and a closure plug 673 which closes the right end of the bore. Thus, G1 pressure acting leftward on the full end area of the G1 governor plug 660 provides this bias only when the flow valve 628 is in its no-flow position with no range shift occurring or in its lockup cutoff position on the occurrence of a range shift but with modulator valve 646 in its bypass position below the predetermined part engine throttle opening. When the flow valve 628 is in its lockup cutoff position with the occurrence of a range shift and the flow valve modulator valve 646 is in its exhaust position below part engine throttle opening, the G1 pressure is exhausted from the lockup valve 654. An exhaust 671 prevents hydraulic lock between plug 660 and valve element 658.

A controlled fluid pressure bias at the lockup valve 654 which assists the fixed bias of spring 666 in opposing the G1 pressure bias is normally provided by the TV pressure and is assisted by the T pressure when the latter becomes available. When the lockup valve element 658 is in the release position shown, the TV line 594 is connected past land a to chamber 674 in the left end of the bore. The T line 604 is connected by a ball check valve 676 to the chamber 674 and the chamber is always connected through an orifice 678 to an exhaust 680. The orifice 678 maintains the pressure in chamber 674 when it is receiving fluid and relieves the chamber of pressure when there is no supply. The check valve 676 prevents TV pressure from reaching the T line 604 during the time when no T pressure exists which occurs during zero and part engine throttle opening (-40 percent travel of the primary TV valve element 587).

When converter turbine speed is sufficient to allow lockup clutch operation, G1 pressure which is proportional to converter turbine speed is sufficient to move the lockup valve element 658 leftward to its apply position. The TV pressure which is always available beyond closed engine throttle admitted to chamber 674 past land a inhibits the initial leftward movement of the lockup valve. As the lockup valve element 658 moves leftward, land 0 blocks delivery of TV pressure and the chamber 674 is exhausted through orifice 678 to provide further leftward movement by snap action against the spring bias after TV pressure has been overcome. Thus, when the lockup valve element 658 is in its apply position and T pressure is not avilable, lockup clutch release is delayed by requiring a lower G1 pressure (lower converter turbine speed) to enable the spring bias to move the lockup valve element to its release position.

The T pressure which is provided by TV pressure only from 40 percent through 100 percent travel of the primary TV valve element 587 is delivered through the check valve 676 to chamber 674 of the lockup valve 654. T pressure below its maximum value delays lockup clutch apply by requiring a higher G1 pressure (higher converter turbine speed) to move the lockup valve element 658 to its apply position. T pressure at its maximum value 100 percent travel of the primary TV valve element 587 with engine throttle open through detent) prevents movement of the lockup valve element 658 to its apply position when it is in its release position and forces movement of the lockup valve element to its release position when it is in its apply positron.

The lockup valve 658 in its apply position connects the main line 510 between lands b and c to the lockup clutch line 668 to engage the lockup clutch 238 and also to urge the main pressure regulator valve element 520 leftward to allow more fluid to flow into the lubrication line 546, such added regulator valve bias effecting a reduction in main pressure which is permissible because lower torque at higher rotating speeds is being transmitted by the power train under these conditions. The lockup valve 658 in its apply position also connects the converter signal line 672 between lands a and b to an exhaust 682 so that the converter pressure regulator valve 442 regulates at the low value which is possible since with the lockup clutch applied, there is no heat being generated in the torque converter.

FORWARD AND REVERSE SHIFT VALVE The forward and reverse main line 566 in addition to directing forward and reverse main pressure to the two TV valves 580 and 582, also directs this pressure to a forward and reverse shift valve 684 shown in H0. 2e. The forward and reverse shift valve 684 is for connecting the forward and reverse main line 566 to either a forward clutch line 686 which delivers the pressure to a motor 688 operating the forward drive clutch 246 or to a reverse clutch line 690 which delivers the pressure to a motor 692 operating the reverse drive clutch 252. The forward and reverse shift valve 684 has a valve element 694 having lands a, b c and d of equal diameter located in a bore 696 in the valve body. The shift valve element 694 is mechanically dentented by diametrically opposed spring loaded balls 698 which engage with either one of a pair of concave surfaces between lands c and d to hold the shift valve element in either its reverse clutch apply position as shown or its forward clutch apply position.

In the reverse clutch apply position the forward and reverse main line 566 is connected between lands b and a to the reverse clutch line 690 to apply the reverse drive clutch 252. At the same time, the forward clutch line 686 'is connected between lands a and b to the lubrication line 546 which receives the overage from the main pressure regulator valve 518. The pressure in lubrication line 546 is regulated by a lubrication pressure regulator valve 700 shown in FIG. 2c which has a valve element 702 normally biased to the closed position shown by a regulator spring 704. Pressure in the lubrication line 546 is maintained by regulating action of valve 700 which opens against the spring bias to permit all fluid in excess of that required to maintain lubrication pressure and flow to return to the reservoir via exhaust 706. The regulated lubrication pressure in the lubrication line 546 is low enough so that the fluid at this pressure fills the forward clutch motor 688 but does not effect forward clutch engagement to thus ready the disengaged forward drive clutch for subsequent engagement.

When the forward and reverse shift valve element 694 is moved to the right to the forward clutch apply position through the mechanical detent, the forward and reverse main line 566 is connected between lands a and b to the forward clutch line 686 to apply the forward drive clutch 246. The reverse clutch line 690 is then connected between the lands b and c to the low pressure lubrication line 546 to release the reverse drive clutch 252 while the reverse clutch line 690 and reverse clutch motor 692 are maintained full of fluid at the low lubrication pressure in readiness for subsequent reverse drive clutch engagement.

The positioning of the forward and reverse shift valve element 694 is controlled by fluid pressure bias. The valve bore 696 is closed at both ends providing chambers 710 and 712 at the opposite ends of the valve element 694. Chambers 710 and 712 are simultaneously supplied with fluid from the forward and reverse main line 566 via orifices 713 and 714, respectively, as subsequently described and their closure and exhaust is selectively provided by solenoid valves 715 and 716, respectively. The chambers 710 and 712 are connected to control lines 718 and 720, respectively, and both of the solenoid valves 715 and 716 are normally de-energized in which condition they are closed and block the control lines 718 and 720 from exhausts 722 and 723, respectively, to thus close the chambers. The chambers 710 and 712 when supplied from the forward and reverse main line 566 then have full forward and reverse main pressure which acts on the full end area of lands a and d and thus there is a fluid pressure balance on the valve element 694 and the mechanical detent 698 holds the valve in one of its two positions. The solenoid valves 715 and 716 have internal orifices larger than the orifices713 and 714 and upon energization of one of the solenoid valves it will be opened and exhaust one chamber of pressure through its internal orifice permitting the retained pressure on the other end of the forward and reverse shift valve element 694 to move the valve through the mechanical detent into the other detented position. With the forward and reverse shift valve 684 in the reverse clutch apply position shown, energization of the solenoid valve 716 exhausts chamber 712 of pressure permitting the retained pressure acting in chamber 710 to move the valve rightward through the detent to the forward clutch apply position. Alternatively, energization of the solenoid valve 715 exhausts chamber 710 permitting the retained pressure in chamber 712 to move the valve leftward to the reverse clutch apply position.

FORWARD AND REVERSE SHIFT INHIBITOR VALVE A forward and reverse shift inhibitor valve 724 shown in F IG. 2e permits the forward and reverse shift valve 684 to shift the power train between forward and reverse in the first drive range and prevents shifting between forward and reverse in all higher drive ranges. The forward and reverse shift inhibitor valve 724 has a valve element 726 with lands a and b of equal diameter located in a bore 728 in the valve body. The valve 724 further has a G2 plug 730 and a stop plugv 732 both of the same diameter as lands a and b located in the bore 728. A spring 734 normallybiases the valve members leftward to the position shown with plug 732 acting as a stop. In this position which is the forward-reverse shift permit position the forward and reverse main line 566 is connected through the valve 724 between its lands a and b and then through the orifices 713 and 714 to the respective chambers 710 and 712 of the forward and reverse shift valve 684. Thus, with the forward and reverse shift inhibitor valve 724 in its forward-reverse shift permit position, the forward and reverse shift valve 684 may be operated by its solenoid valves 715 and 716 to selectively apply the forward drive clutch 246 and the reverse clutch 252.

Forward-reverse shift prevention is provided by connecting the G2 line 577 to deliver G2 pressure to a chamber 736 where it acts on the full left end area of the G2 plug 730 to urge the G2 plug and valve element 726 rightward against the spring bias to an inhibit position in which land a of the valve element blocks the forward and reverse main line 566 at the upstream side of the valve and connects the forward and reverse main line 566 at the downstream side to an exhaust 740. With both chambers 710 and 712 of the forward and reverse shift valve 684 thus exhausted by the forward and reverse shift inhibitor valve 724, operation of the solenoid valves 715 and 716 is ineffective to shift the forward and reverse shift valve 684 from the position it then occupies which will either be forward or reverse. Since G2 pressure is proportional to the range unit output speed which is zero throughout the first drive range, no G2 pressure is delivered to the forward and reverse shift inhibitor valve 684 during first drive range operation in either forward or reverse and thus the forward and reverse shift inhibitor valve will be in its permit position as shown to permit the operator to shift the power train between forward and reverse in the first drive range. Exhausts 740, 742 and 744 are provided to prevent hydraulic lock in the forward and reverse shift inhibitor valve 724.

When the vehicle is moving in either the forward or reverse direction in either the second, third or fourth drive range the G2 pressure is always present and conditions the forward and reverse shift inhibitor valve 724 in its inhibit position to prevent the forward and reverse shift valve 684 from effecting shifts between forward and reverse. Thus, the operator is prevented from making a shift between forward and reverse in the second, third and fourth drive range which might overload the power train, shifts between forward and reverse in the first drive range being permitted for rocking the vehicle in low traction situations.

SEQUENCE VALVE A sequence valve 746 shown in FIG. 2e is for disengaging the low low brake 318 during shifts between the first forward and first reverse drive range to permit engagement of the directional clutches (clutches 246 and 252) under no load conditions recalling that directional changes are prevented in the second, third and fourth drive range in forward and reverse by the forward and reverse shift inhibitor valve 724. The sequence valve 746 has a valve element 748 having lands a and b of equal diameter and a plug 750 of the same diameter located in a bore 752 in the valve body. The valve elements 748 and 750 are biased rightward by a spring 754 to the position shown which is the release position. In the release position, a 1-2 line 756 which normally connects the range line 626 to engage the low low brake 318 as described in more detail later is connected between the lands a and b of valve element 748 to an exhaust 758 to release the low low brake 318.

The forward clutch line 686 and reverse clutch line 690 from the forward and reverse shift valve 684 are continuously connected to the bore 752 of the sequence valve 746 at the right end of plug 750 and between valve element 748 and plug 750, respectively.

Thus, when the reverse drive clutch 252 is engaged with the forward and reverse shift valve 684 in the reverse clutch apply position shown, forward and reverse main pressure acts on both the full right end area of land b of the valve element 748 and the full left end area of plug 750 while the lower lubrication pressure acts on the full right end area of valve plug 750. The fluid pressure imbalance on plug 750 holds it in the position shown and the fluid pressure on valve element 748 moves it leftward against the spring bias to a normal apply position. In the normal apply position, land b of valve element 748 blocks exhaust 758 and the 1-2 line 756 is connected through the valve between lands a and b for main pressure transmittal to engage the low low brake 318. When the forward and reverse shift valve 684 is operated to change vehicle direction from reverse to forward in the first drive range which normally has the low low brake 318 engaged, the forward clutch line 686 is supplied with fluid from the forward and reverse main line 566 which fluid is also admitted to act on the right end of plug 750 while thereverse clutch line 690 is filled with lubrication fluid which is also admitted to act on the right end of land b and on the left end of plug 750. As the forward clutch 246 is engaged and with the leftward acting fluid pressure on the valve element 748 thus reduced to the low lubrication pressure, the leftward acting pressure on plug 750 is below the normal forward and reverse main pressure because of the flow requirements for the clutch engagement. This permits the spring 754 to move the valve element 748 rightward to its release position against plug 750 which remains to the right so that while the forward drive clutch 246 is being engaged, the 1-2 line 756 is exhausted through exhaust 758 to drop out or release the low low brake 318. The pressure in the forward clutch line 686 rises with engagement of the forward drive clutch until full forward and reverse main pressure is reached. Full forward and reverse main pressure or a slightly lower pressure is effective to move plug 750 and the contacting valve element 748 leftward to reestablish connection of the l-2 line 756 through the valve and thus reestablish engagement of the low low brake 318.

When the forward and reverse shift valve 684 is operated to change vehicle direction from forward to reverse in the first drive range, the fluid from the forward and reverse main line 566 is admitted to act on the right end of land b of valve element 748 and the left end of plug 750 while lubrica-tion fluid is admitted to act on the right end of plug 750. As the reverse drive clutch 252 is engaged and with the, leftward acting pressure on the plug 750 thus reduced to the low lubrication pressure, the fluid pressure acting leftward on the valve element 748 and rightward on the plug 750 is below the normal forward and reverse main pressure because of the flow requirements for the clutch engagement. This permits the spring 754 to move the valve element 748 and contacting plug 750 rightward to the release position so that while the reverse drive clutch 252 is being engaged, the low low brake 318 is released. The pressure in the reverse clutch line 690 rises with engagement of the reverse drive clutch until full forward and reverse main pressure is reached. Full forward and reverse main pressure or a slightly lower pressure is effective to move valve element 748 leftward to its apply position to reestablish engagement of the low low brake 318 while the plug 750 is held to the right by its pressure imbalance.

NEUTRAL sHIFr VALVE A neutral shift valve 759 shown in FIG. 2b is for conditioning the power train in neutral and has a valve element 760 having lands a and b of equal diameter located in a bore 762 in the valve body. A spring 764 urges the valve element 760 toward the neutral position shown in which land a blocks the range main line 626 upstream of the valve and connects the range main line downstream of the valve between the lands a and b to an exhaust 768. The forward and reverse main line 566 is connected through an orifice 770 to a chamber 772 at the right end of the valve element 760. A solenoid valve 774 is connected by a control line 776 to the chamber 772 and when de-energized blocks the line 776 and thus chamber 772 from an exhaust 778. When the chamber 772 is thus blocked, the chamber is filled through orifice 770 and the pressure rises to full forward and reverse main pressure This pressure acts on the full end area of land b and is effective to move the valve element 760 leftward to a range shift position. The valve element 760 in the range shift position connects the range main line 626 through the valve between lands a and b while land b blocks exhaust 768, an exhaust 779 preventing hydraulic lock in the valve.

When the solenoid valve 774 is energized it connects the chamber 772 via the line 776 to the exhaust 778 through an internal orifice larger than orifice 770 to prevent pressure buildup in the chamber which is being continuously fed through orifice 770. This pressure exhaust permits the spring 764 to move the valve element 760 to its neutral position blocking the range main line 626 at the upstream side and exhausting the downstream range main line.

MANUAL SIGNAL VALVE A manual signal valve 780 shown in FIG. 2b provides selective delivery of forward and reverse main pressure for manually controlled shifts to all the drive ranges below the highest (1 2 and 3) and T pressure for all automatic'shifts. The manual signal valve 780 has a valve element 782 having lands a, b and c of equal diameter located in portion 784 of a stepped bore 785 in the valve body and a land d of smaller diameter located in bore portion 788. A spring 790 biases the valve element 782 rightward toward the manual signal position shown. In this position, the T line 604 is blocked at the upstream side of the valve by land a and is connected at the downstream side of the valve between the lands a and b to an exhaust 789. In addition, the forward and reverse main line 566 is connected in the manual signal position through the manual signal valve between lands b and c.

Theforward and reverse main line 566 upstream of the manual signal valve 780 is always connected 

1. In a control system for a power train the combination of variable ratio hydrostatic drive means including a pump and motor for providing a variable drive ratio controlled by control pressure delivery thereto; a fluid pressure source; control pressure regulator valve means operatively connected to said fluid pressure source for providing a control pressure increasing with increasing pump outlet pressure; steer valve means for controlling delivery of said control pressure to said hydrostatic drive means to vary the drive ratio; limiter valve means for limiting the drive ratio normally determined by said steer valve means according to a predetermined pressure differential across said pump; relief valve means for limiting pump outlet pressure; and relief valve modulator valve means operatively connected to said relief valve means for increasing the limit on pump outlet pressure with increasing torque demand and decreasing output speed.
 2. In a control system for a power train the combination of variable ratio hydrostatic drive means including a pump and motor operatively connected by two pump-motor fluid lines; pump stroke control means including a pair of oppositely acting fluid motors for fixing pump displacement when said fluid motors are pressure balanced and varying pump displacement when said fluid motors have a pressure imbalance; a fluid pressure source; control pressure regulator valve means operatively connected to said fluid pressure source and both said pump-motor fluid lines for providing a control pressure increasing with increasing pump output pressure in either of said pump-motor lines; steer valve means for controlling delivery of said control pressure to said fluid motors to selectively provide a control pressure balance at said fluid motors to fix pump displacement and a control pressure imbalance at said fluid motors to vary pump displacement; stroke limiter valve means operatively connected to both said pump-motor lines and operatively connected between said steer valve means and one of said stroke fluid motors for substituting pump outlet pressure in place of control pressure at said one fluid motor to prevent increase in pump displacement producing motor drive in one direction in response to a predetermined pressure differenTial across said pump and substituting pump inlet pressure in place of control pressure at said one fluid motor in response to said predetermined pressure differential acting oppositely across said pump to prevent increase in pump displacement producing motor drive in the opposite direction. 